Not Applicable.
1. Field of the Invention
The present invention relates generally to systems used in elevators for encoding the identity of various input/output (xe2x80x9cI/Oxe2x80x9d) devices. In particular, the present invention concerns systems and methods for reducing the memory and bandwidth requirements of an electronic elevator system by uniquely identifying various elevator I/O devices with a 2-byte identification field.
2. Description of the Related Art
An elevator includes a car for moving passengers or freight between various landings, or floors, using various drive systems such as a traction drive system or a hydraulic system. The movement of the car is controlled by a controller comprising one or more computers, which must communicate with various I/O devices. Devices in the elevator system are generally located in three places: a machine/power-unit room; the car; and a hallway near the landings. In addition to the controller for the drive system, the devices include the floor selection buttons inside the car, the hall call buttons, the hall and car lanterns, the drive motor for opening and closing the car door, a selector for determining certain parameters such as the car location, speed and direction, various sensors, and the safety equipment of the elevator.
Traditionally I/O devices were connected to the controller through discrete wiring. A separate wire was needed to connect each I/O device to the controller. Thus, if the controller were located in a swing return, all I/O devices from the hall and power-unit room needed to be connected via a traveling cable. In order to reduce the number of discrete wires running from the hall and the car to the controller, some elevator manufacturers began using a distributed I/O system.
In a distributed I/O system, there must be a common protocol for communicating between intelligent I/O devices and the controller. Various communications protocols have been developed to allow a computer to communicate with multiple I/O devices over a serial link. Because the I/O devices are linked serially, any protocol used with the system must provide a means for identifying the sending and receiving I/O device, as well as a means for sending data and messages. One well-known protocol that has been used in elevator equipment is LonTalk.(copyright)
The LonTalk(copyright) protocol, which is described in U.S. Pat. No. 5,513,324 to Dollin, Jr. et al., the disclosure of which is hereby incorporated by reference, provides a framework for communicating between intelligent I/O devices and the controller. In some areas, this framework is completely defined, while in other areas some flexibility is provided. LonTalk(copyright) uses Standard Network Variable Types (xe2x80x9cSNVTsxe2x80x9d) to allow many types of information to be sent. Unfortunately, there are no SNVTs available that are suitable for identifying standard elevator I/O devices. Therefore, elevator manufacturers using LonTalk(copyright) have had to develop their own network variables. Present systems use an ASCII encoding system to identify various I/O devices. In such elevator systems, each I/O device is identified by a mnemonic. For example, Fire Service Call Cancel is identified by the mnemonic xe2x80x9cFSCCxe2x80x9d.
One problem with present systems that use ASCII encoding is that each letter of the mnemonic takes a byte of data. Because the operation of elevators involves sending large numbers of data packets, it would be desirable to provide a more efficient way of identifying I/O devices. It is thus an object of the present invention to reduce the number of bytes necessary to identify uniquely each I/O device within the elevator system. This would help minimize the length of the messages being sent between devices, and consequently speed up communications and reduce the systems memory requirements.
An elevator system according to the invention has a control processor that communicates with numerous I/O devices over a serial communications link. The processor is programmed to generate and receive data packets containing a 2-byte I/O identification field. The first byte is a general category representing the type of function performed by the I/O device, and the second byte represents the identity of the particular I/O device within such group. The I/O devices similarly generate and receive data packets containing the 2-byte I/O identification field. By way of example, categories may represent such functions as car call inputs, car call outputs, code blue inputs, code blue outputs, fire service, and so on. For a category such as car call inputs, the car call button for each floor would be assigned a separate sub-category designation. The invention reduces the amount of memory required by the distributed electronics and limits the amount of bandwidth used in identifying each I/O device on the serial link.